(CNN)Brandon Stanton, the blogger and photographer behind the popular project "Humans of New York," denounced Donald Trump as "hateful" in an open letter on Monday, charging the Republican primary front-runner with seizing on racial division and religious prejudice to advance his campaign.

"I've watched you retweet racist images. I've watched you retweet racist lies. I've watched you take 48 hours to disavow white supremacy. I've watched you joyfully encourage violence, and promise to 'pay the legal fees' of those who commit violence on your behalf," Stanton said, explaining why he chose to go public with his concerns despite trying "my hardest not to be political."

The Trump campaign did not immediately respond to a request to comment.

Stanton began "Humans of New York," an online compilation of viral photographs and personal interviews with city dwellers begun, in 2010. Three years later, he cataloged his work in a New York Times bestselling book.

In 2015, Stanton traveled to Turkey and Jordan, where he met with a series of refugee families as they sought to leave the region for the United States.

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"The tragedy of their stories, learning what they experienced in Syria and Iraq, has been completely eye-opening to me," he told CNN's Fareed Zakaria at the time. "It is a story I want to be able to tell to my audience."

Among them: President Barack Obama, who in September 2015 commented on the "inspirational story" he found in a "Humans" Facebook post from Iran.

On Monday, Stanton referenced his time overseas and what he learned from speaking with "with hundreds of Muslims."

"I've also interviewed hundreds of Syrian and Iraqi refugees across seven different countries," he wrote. "And I can confirm -- the hateful one is you."

Trump in December called for a temporary ban on all Muslims trying to enter the U.S., including refugees.

The Republican presidential front-runner, who has previously called for surveillance against mosques and said he was open to establishing a database for all Muslims living in the U.S., made his latest controversial call in the wake of a deadly mass shooting in San Bernardino, California, by suspected ISIS sympathizers.

And in an interview with Jake Tapper on CNN's "State of the Union" last month, Trump balked at condemning former Ku Klux Klan grand wizard David Duke and other white supremacist supporters. The billionaire later said he couldn't hear the question, blaming a "bad earpiece," and disavowed the groups amid public outrage.

On Sunday, he told NBC's "Meet the Press" he would consider footing any legal fees incurred by a man who was arrested after sucker-punching a protester at a campaign rally in North Carolina last week.